JPH033417B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a photoelectric switch that utilizes reflected light from an object to be detected.

[Background Art] This type of photoelectric switch includes a diffuse reflection type that detects the presence of an object based on the presence or absence of reflected light, as shown in Figure 3a, and a diffuse reflection type that detects the presence of an object based on the presence or absence of reflected light, as shown in Figure 4a and b. There is a distance detection type that detects the distance to an object based on the angle of incidence on the light receiving section.

First, in the diffuse reflection type, as shown in Figure 3a, the light receiving element 2 receives the diffuse reflection light from the object surface, converts it into a voltage signal in the light receiving circuit 3, logarithmically transforms it in the logarithmic amplifier circuit 4, and converts the light into a voltage signal. The output Vin is input to the object detection comparison circuit 5 and compared with the detection level setting voltage Va for adjusting sensitivity, and when Vin is larger, a detection signal is output. The signal processing circuit 9 uses the synchronization signal from the oscillation circuit 14 to sample the output of the comparator circuit 5 at the timing when the drive circuit 13 is generating the light beam P from the light projecting element 11 to remove external light noise. The output of this signal processing circuit 9 is applied to an output circuit 15 consisting of a relay or the like and a detection display section 16. Further, the margin display section 17 is for displaying whether there is a margin between the received light signal level and the operating limit level, in other words, whether or not cleaning of the lens is required. A margin display set voltage Vb with a little margin than the above-mentioned detection level set voltage Va is output, and the margin display comparison circuit 8 compares the received light signal voltage with this margin display set voltage Vb, and the output of the comparison circuit 8 is The lighting of the margin display section 17 is controlled by.

Figure b shows the configuration of the logarithmic amplifier circuit 4, which includes an operational amplifier _G0 and a feedback diode.
By logarithmically converting the received light signal output using D ₀ , the distance to the object and the detection signal level are made proportional, expanding the dynamic range and enabling highly accurate detection.

However, the above conventional configuration has the following problems. In other words, the reason why the detection level setting circuit 6 and the margin level setting circuit 7 are provided individually is as follows.
This is to set the detection level setting voltage Va and margin display setting voltage Vb independently of each other, and both setting circuits 6 and 7 are configured as shown in FIG. As shown,
The signal generated by constant current source J ₁ or J ₂ is logarithmically converted by a logarithmic amplifier consisting of operational amplifiers G ₁ , G ₂ and silicon diodes D ₁ , D ₂ , and the output voltages Va and Vb are sent to respective comparison circuits 5 and 8
is being entered. In other words, the logarithmic amplifier circuit 4 uses the logarithmic characteristics of a recon diode, and its temperature characteristics depend on changes in carrier concentration due to changes in the temperature of the PN junction. Even if the reference level setting circuit of 6 and 7 is configured with an inexpensive temperature compensation circuit using a thermistor, it is impossible to provide the same temperature characteristics as the logarithmic amplifier circuit 4, and both level setting circuits 6 and 7
This is because there is no appropriate temperature compensation method unless the same circuit as the logarithmic amplifier circuit 4 is used. However, using a logarithmic amplifier for each level setting circuit in this way requires a high-precision operational amplifier for each, which is extremely uneconomical.

Next, in the distance detection type, as shown in FIG. When the reflected light R is diffusely reflected on the surface of the detected object Detected object X
As shown in Figure b, the circuit configuration consists of two light-receiving elements 2a and 2b or a semiconductor position detection element (PSD ) are converted into signal voltages by the light receiving circuits 3a and 3b, and further logarithmically converted by the logarithmic amplifier circuits 4a and 4b, and then inputted to the differential amplifier circuit 18, and the difference output is sent to the distance detection comparison circuit 19. As signal input Vd,
Reference voltage supplied from detection distance setting circuit 20
It is compared with Vc. In this case as well, one of the two logarithmic conversion circuit outputs, Vin, is input to the margin display comparison circuit 8 to display whether there is sufficient margin between the received light signal level and the operating limit level. After the indicator lamp goes out, it is necessary to display whether or not operation is possible without malfunction by detecting whether the received light signal level is higher than the operating limit level, and for this purpose, the operation display comparison circuit 21 and an operation display section 22 are required.

In the above configuration, the distance detection comparison circuit 19
By taking the difference between the outputs of the logarithmic amplifier circuits 4a and 4b, the input signal Vd of the input signal Vd is canceled out by each other, and therefore the detection distance setting circuit 20 does not require a logarithmic amplifier. , an operation level setting circuit 23 and a margin level setting circuit 7 for supplying reference voltages to the operation display comparison circuit 21 and the margin display comparison circuit 8, respectively, have a logarithm for compensating for the temperature error of the logarithm conversion output Vin. This requires an amplifier, and as in the case of the diffuse reflection type shown in FIG. 3, there is a problem in that an expensive logarithmic amplifier is required for each setting circuit.

[Object of the Invention] The present invention has been made in view of the above-mentioned problems, and its purpose is to be able to perform appropriate temperature compensation for a logarithmic amplifier circuit, and to
It is an object of the present invention to provide a circuit configuration of a level setting section that can generate mutually independent reference levels to be supplied to a plurality of comparison circuits using a single logarithmic amplifier.

[Disclosure of the Invention] Accordingly, the present invention logarithmically converts the light reception signal of reflected light from a detected object using a logarithmic amplifier circuit, and compares the logarithmically converted output with a first reference level setting voltage using a first comparison circuit. At the same time, in the photoelectric switch in which the logarithmically converted output is compared with a second reference level setting voltage in a second comparator circuit, the output ends of the logarithmic amplifiers that logarithmically convert the reference voltage are connected through level setting resistors. It is characterized in that it is connected to the reference input terminal of both of the comparison circuits mentioned above, and that a current is supplied to each resistor from a constant current source, so that the voltage at the output terminal of the logarithmic amplifier in the level setting section is This makes it possible to set a plurality of reference levels using a single logarithmic amplifier without being affected by the value of the level setting resistor or the value of the current supplied to the resistor from a constant current source.

FIG. 1 shows an embodiment of the photoelectric switch of the present invention. In the figure a, the output current of the light receiving element 2 is converted into a voltage signal by the light receiving circuit 3, further logarithmically converted using the logarithmic amplifier circuit 4, and the output signal Vin is inputted to the first comparison circuit 5. , the first reference level setting voltage Va, and the second reference level setting voltage Va.
The comparison circuit 8 compares the light reception signal voltage Vin and the second reference level setting voltage Vb. These first and second comparison circuits 5 and 8 correspond to the object detection comparison circuit 5 and the margin display display comparison circuit 8, respectively, in the diffuse reflection type embodiment shown in FIG. 3a. , correspond to the comparison circuit 21 for operation display and the comparison circuit 8 for margin display, respectively, in the distance detection type embodiment shown in FIG. Level setting voltages Va and Vb are set in a single level setting section 1
It is designed to be supplied from 0.

Figure 1b shows the circuit configuration of the level setting section 10, in which a constant current source is generated by a logarithmic amplifier A consisting of an operational amplifier _G1 and a silicon diode _D1 .
The reference current _I0 generated at _J0 is logarithmically converted, and its output terminal is connected to the first comparator circuit 5 via a resistor _R1 , and also to the second comparator circuit ₈ via a resistor R2. , constant current sources J ₁ and J ₂ are connected to the output side of each resistor R ₁ and R ₂ , respectively. With this configuration, each reference level setting voltage Va and Vb
Va=V ₀ +I ₁ ×R ₁ Vb=V ₀ +I ₂ ×R ₂ and can be obtained by level-shifting the logarithmically converted reference voltage V ₀ by an arbitrary value. Furthermore, by making the resistance values R ₁ and R ₂ or the current values I ₁ and I ₂ variable, each can be adjusted without affecting the other set levels.

Furthermore, the above embodiment uses a single logarithmic amplifier to supply two types of reference levels; Operating limit levels may be required. The embodiment shown in FIG. 2a shows a case where the number of comparison circuits is increased to three or more, and in this case also constant current sources J ₁ to J ₅
By making the current value or each resistance value R ₁ to R ₅ variable, the respective setting levels can be adjusted without affecting each other. Figure b shows the light reception signal when detecting an object.
It shows the relationship between Vin and each set voltage _V1 to _V5 .

[Effects of the Invention] As described above, the present invention provides a photoelectric switch equipped with a plurality of comparison circuits for comparing the level of reflected light from a detected object with a plurality of reference levels. Since the reference levels can be supplied independently from each other, there is no need to perform temperature compensation for the logarithmic amplifier circuit provided for each comparison circuit to expand the dynamic range of the received light signal, and an individual logarithmic amplifier can be provided. This has the advantage that the number of expensive operational amplifiers used can be reduced compared to the conventional example.

[Brief explanation of the drawing]

Figure 1a is a block diagram of one embodiment of the photoelectric switch of the present invention, b is a circuit diagram of the same essential parts as above, Figure 2a is a circuit diagram of the essential parts showing another embodiment of the photoelectric switch of the present invention, Fig. 3a is a block circuit diagram of a conventional photoelectric switch, b and c are circuit diagrams of the same main parts, Fig. 4a is a diagram explaining the principle of another conventional example, and b is a block diagram of the same as above. It is. 1 is a light receiving optical system, 2 is a light receiving element, 3 is a light receiving circuit, 4 is a logarithmic amplifier circuit, 5 is a first comparison circuit or a comparison circuit for object detection, 6 is a detection level setting circuit, 7 is a margin level setting circuit, 8 is a second comparison circuit or a margin display comparison circuit, 9 is a signal processing circuit, 10 is a level setting section, 11 is a light projecting element, 12
13 is a light projection optical system, 13 is a drive circuit, 14 is an oscillation circuit, 15 is an output circuit, 16 is a detection display section, 17
18 is a differential amplifier circuit, 19 is a comparison circuit for distance detection, 20 is a detection distance setting circuit, 21
is the first comparison circuit or the operation display comparison circuit;
2 is an operation display section, 23 is an operation level setting circuit, A
is a logarithmic amplifier, G ₀ , G ₁ , G ₂ are operational amplifiers, D ₀ ,
D ₁ and D ₂ are silicon diodes, J ₁ to J ₅ are constant current sources, R ₁ to _{R 5} are resistors, Vin is logarithmic conversion output, Va is the first reference level setting voltage, and Vb is the second reference level. Setting voltage.

Claims (1)

[Claims] 1 Logarithmically converts the light reception signal of the reflected light from the detected object in a logarithmic amplifier circuit, compares the logarithmically converted output with a first reference level setting voltage in a first comparator circuit, and converts the logarithmically converted output into a second The second comparison circuit
In a photoelectric switch designed to compare the reference level setting voltage of A photoelectric switch characterized in that a current is supplied from a constant current source to each of the switches.